1. Field of the Invention
This invention relates to thermal energy storage and utilization and more particularly to a system for storage of thermal energy in especially configured liquid containing tanks.
2. Description of the Prior Art
The attention which has only recently been directed to the various problems relating to energy has caused some concern as to the wasteful and otherwise inefficient manner in which energy is employed to accomplish the many tasks upon which society has come to depend. The equipment and techniques currently being employed to accomplish those tasks have more or less evolved rather than being the result of a plan, and since much of this evolution took place in an era of plenty, very little effort has been expended on the efficiency of such techniques and equipment.
In particular, the various types of equipment currently being employed to perform heating and cooling tasks operate on what may be called a demand basis, and such a technique results in wasted energy and other energy related problems. These problems resulting from the demand basis technique may be placed in three major problem areas with the first being demand timing, the second being the intermittent delivery and the third being the fluctuating amounts of energy that must be supplied to satisfy the demand.
To explain the term demand basis, consider a home which is either too hot or too cold. That fact is sensed by a thermostat which actuates the appropriate equipment and when the demand has been satisfied, the equipment is shut down.
With regard to the first problem area defined above as demand timeing, the demand for heating and/or cooling invariably occurs at times when those tasks are most inefficiently accomplished. For example, it is well known that a heat pump is an efficient mechanism; however, the demand basis under which the heat pump is forced to operate substantially reduces the efficiency of that equipment. During a heating cycle, the heat pump will extract heat from the atmosphere and direct it to the zone being heated. The demand for heat in the zone is of course, the greatest when the temperature is low and the atmosphere contains a relatively small amount of readily available heat. Due to this lack of readily available heat during the peak demand time, the heat pump must work hard to accomplish the task being asked of it. The same basic inefficiency exists during a cooling cycle of the heat pump due to the heat extracted from the zone being dissipated into an atmosphere that already contains a relatively large quantity of heat. Thus, to accomplish satisfactory operation under such conditions, the equipment must be relatively large to compensate for the inefficient operation resulting from demand timing and it is readily apparent that operating equipment inefficiently results in the consumption of power at a rate which is excessive for the amount of work being accomplished.
In regard to the second problem area defined above as intermittent delivery, consider a zone being heated with the thermostat set at 70 degrees. Due to intermittent delivery, the temperature in the zone will vary in a range of from about 67 to 74 degrees. When the temperature in the zone falls to about 67 degrees, the heating equipment is started and will continue to operate until the zone temperature reaches about 74 degrees at which time the equipment is shut off. The temperature will then drop until the 67 degree level is reached again and the heating cycle is repeated. This temperature drop is nonlinear due to the varying heat loss at the different temperatures, with the heat loss being considerably greater at 74 degrees than at the lower temperatures. It is well known that heat loss through walls, ceilings, windows and the like is determined by the temperature differential on opposite sides thereof. Thus, the temperature drop from 74 degrees to 70 degrees will be relatively rapid and will slow down in the drop from 70 degrees to 67 degrees. The zone will therefore fluctuate in temperature and will be below the desired 70 degrees level the greatest percentage of the time. It will be obvious that the exact opposite temperature fluctuations will occur when a zone is being cooled. Such temperature fluctuations in conjunction with the duration of the undesirable temperatures results in discomfort often resulting in upward or downward adjustments of the thermostat. Such discomfort is but one drawback of an intermittent delivery system with other drawbacks being the relatively high power consumption and heat loss or heat gain of such a system when compared with one of constant delivery. The power consumed in repeatedly starting and stopping equipment is well known to be greater than the power consumed in continuous operation thereof. Also, repeated actuation of such equipment to raise or lower the temperature utilizes more energy than constantly delivering properly conditioned air to maintain the desired temperature. By maintaining a constant comfortable temperature, the increased heat loss or heat gain which occurs at fluctuating temperatures is avoided.
The third problem area relating to the fluctuating amounts of energy supplied to satisfy the demand basis technique will be easily understood upon reconsideration of the hereinbefore described examples relating to heating and cooling. It has been established that the demand for heating and cooling is the greatest when it is the most difficult to accomplish those tasks. Those demands plus other energy consuming habits of the consumers cause tremendous fluctuations in energy consumption to occur over a given time period. For example, in hot weather, electric power generating facilities will be operating at or near capacity from approximately 3:00 P.M. to 8:00 P.M. and will be operating considerably below capacity at other times of the day. Such inconsistent energy demands cause problems for the utility companies and such problems result in higher rates for the consumer as well as possible energy curtailment.
Briefly, the fluctuating energy consumption as described above results in problems for the utility companies in that their ability to meet the demand during peak demand periods is constantly being reduced as the demand for energy increases. Until recently, this presented no problems in that when the demand went up the utilities simply acquired more fuel for the production of energy or built more power generating facilities. Such solutions are no longer a simple matter due to environmental considerations, availability of fuel to distribute to consumers or to operate generating equipment, the greatly increased cost of building facilities, and the like.
Since the problems of supplying more energy are extremely difficult to solve, the utilities and others are looking to methods for decreasing the peaks of fluctuating power demands. One method currently being studied is a dual pricing system for encouraging consumers to voluntarily spread out their energy demands. Another method being considered is to force the consumer to reduce his demand during peak demand periods by shutting off power to selected energy consuming equipment during those peak periods.
As described above, the prior art techniques do not utilize energy in an efficient manner, and in addition to those techniques being inefficient, the various types of energy consuming devices employed do not ease the problem. Those devices are, in general, single energy form utilization mechanisms and thus lack the versitility needed to accomplish their tasks by employing energy in various forms when those energy forms are efficiently and economically available. For example, a gas operated heater as we know it today, derives its heating capability solely from gas and lacks the capability of deriving heat from any other energy forms such as electric, solar, or the like. Such lack of versitility can be a serious problem to the consumer in that the tasks he wants his equipment to accomplish simply cannot be accomplished in the event that his single energy form is curtailed for any reason.
Some systems have been devised for the storage and utilization of thermal energy in a more efficient manner and those systems have not been commercially successful heretofore due to the high cost and readily available supply of fossil fuels.
In general, those prior art systems employed a pair of thermal energy storage tanks interconnected by a heat exchanger for transferring thermal energy from one to the other of the tanks to provide a cold and heat storage tank. The tanks are coupled to various thermal energy input and utilization devices.
In addition, the high cost and available fossil fuels, and other factors contributed to the lack of success of those prior art systems. Among those other factors are the high initial costs for construction and the relative low efficiency of the prior art thermal energy storage tanks.
In view of the foregoing, a need exists for a new and useful consumer oriented system for utilizing various forms of energy when readily available and storing the energy for efficient utilization in a manner which overcomes some of the problems of the prior art.